Analog Devices Inc. 5962-9321401MEA

Overview

AD688 from Analog Devices is a high-precision monolithic ±10 V tracking voltage reference IC featuring laser-trimmed thin-film resistors and an ion-implanted buried Zener diode. It delivers 12-bit absolute accuracy (±2 mV initial error), <1.5 mV tracking error, and 1.5 ppm/°C drift over −40°C to +85°C - used as system calibration reference in precision data acquisition and test equipment.

For engineers reviewing the AD688 datasheet, AD688 pinout, AD688 application, or AD688 equivalent, key selection considerations include Kelvin force/sense capability for load regulation, noise reduction pin (6 µV p-p, 0.1–10 Hz), gain/balance trim adjustability, and dual ±10 V output symmetry critical for bipolar DAC/ADC biasing and bridge excitation.

Technical Context

The AD688 integrates a buried Zener reference cell, four laser-trimmed amplifiers (A1–A4), and matched thin-film resistor networks to generate and buffer a precision 20 V span with center-tapped virtual ground. Amplifier A2 senses system ground via Pin 9 (GND SENSE +IN) to establish the reference midpoint, while A3 and A4 provide Kelvin-connected ±10 V outputs with independent force/sense terminals.

Its architecture supports external gain adjustment (Pin 5) and balance centering (Pin 12) without altering Zener operating conditions, preserving low temperature drift. The noise reduction pin (Pin 7) enables optional 1 µF capacitor filtering to reduce broadband noise from 840 µV p-p (1 MHz) to ~250 µV p-p.

Key Specifications

Pinout & Package

AD688 is available in 16-lead CERDIP (Q-16) and wide-body 16-lead SOIC (RW-16) packages. Both are hermetic or molded plastic housings with 0.300" (CERDIP) or 10.65 mm (SOIC) body width, supporting industrial temperature operation (−40°C to +85°C).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar precision voltage reference applications.

Compared with REF5025 and LT1021-10, the AD688 uniquely integrates Kelvin-connected ±10 V tracking outputs, laser-trimmed drift, and onboard low-noise buffers - eliminating external components while delivering guaranteed 12-bit accuracy and <1.5 mV tracking error in a single monolithic IC.

Availability

AD688 is available at Aetrix Electronics and suitable for precision data acquisition, automated test equipment, bridge sensor excitation, and industrial process control requiring stable component supply across extended temperature ranges and long production lifecycles.

Supply support for AD688 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving precision instrumentation, industrial automation, and aerospace markets since 1965.

The AD688 belongs to Analog Devices' precision voltage reference product line, engineered specifically for metrology-grade applications demanding absolute accuracy, low drift, and Kelvin-driven load regulation without external circuitry.

FAQ

What is the maximum load current supported by each output of the AD688?

The AD688 buffer amplifiers A3 and A4 each support ±10 mA output current continuously, as specified in Table 1 under "Output Current A3, A4". This allows direct driving of 1 kΩ loads or multiple 12-bit DACs without external boosting. Exceeding ±10 mA may cause output droop or thermal derating; short-circuit current is rated at 50 mA for fault protection.

Does the AD688 require external capacitors for stability?

The AD688 does not require external capacitors for basic stability - its internal amplifiers are unity-gain stable. However, a 1 µF capacitor on Pin 7 (NOISE REDUCTION) is recommended to reduce broadband noise, and a 20 kΩ resistor between Pin 6 (VHIGH) and Pin 2 (+VS) is mandatory when that capacitor is used to ensure proper startup. No compensation is needed for purely resistive loads ≤1 kΩ.

Can the AD688 be used with a single supply?

No - the AD688 requires dual symmetric supplies (±13.5 V to ±18 V) as specified in Absolute Maximum Ratings and Table 1 test conditions. Its buried Zener reference and fully differential amplifier architecture depend on balanced positive and negative rails; operation with single supply violates biasing requirements and will result in failure to regulate either output.

How does the Kelvin connection improve accuracy in the AD688?

The AD688's Kelvin connections (e.g., Pins 1 & 3 for +10 V) separate force and sense paths so that voltage drops across PCB traces or cables are excluded from regulation feedback. The sense pin monitors voltage directly at the load, causing the amplifier to increase force output until the sensed voltage equals the reference - maintaining ±2 mV accuracy regardless of trace resistance up to several ohms.

What is the purpose of the GAIN ADJ and BAL ADJ pins on the AD688?

GAIN ADJ (Pin 5) adjusts the magnitude of the internal 20 V span to fine-tune +10 V/−10 V absolute accuracy; BAL ADJ (Pin 12) centers the span at true 0 V to minimize tracking asymmetry. Both use 100 kΩ 20-turn potentiometers and preserve low drift because trimming occurs outside the Zener's bias path - the AD688 achieves zero-error calibration without degrading temperature performance.